A sentinel animal which is small and easily handled, to directly detect and measure transmission of leishmaniasis would be extremely valuable for the study of epidemiology and for early recognition of need for control measures. No completely satisfactory sentinel has been available for American cutaneous leishmaniasis. Preliminary studies indicate that Mystromys albicaudatus which is expectionally susceptible to infection and rapidly develops visible lesions, is a candidate for a sentinel to map foci of infection and measure seasonal and annual changes of infection rates. Single sex Mystromys immunized against arbovirus infections will be exposed in 2 ecologically distinct study areas in Panama which have been the source of many human cutaneous/mucocutaneous infections. In Honduras it will be exposed in sites of known kala azar transmission and its value as a sentinel for this disease compared with that of the hamster.